Long-Distance Migration Takes Fuel and Water

Long-distance migration can be hard on a bird’s body. For example, this Swainson’s Thrush might migrate between northern Canada and South America, twice a year. In the weeks before such a long journey and during key stopovers en route, the thrush eats like crazy to put on fat. But during the flight, much of the body’s water supply is used up. To keep flying, a Swainson’s Thrush accesses extra water stored in the proteins of its internal organs and muscles.

In the weeks before such a long journey and during key stopovers en route, the thrush eats like crazy to put on fat. That’s the basic fuel it draws on, by oxidizing fatty acids stored beneath the skin, in the abdomen, and in its muscles. During the intense breathing brought on by the sustained flight, much of the body’s water supply is used up, too. [Swainson’s Thrush call, http://macaulaylibrary.org/audio/119447 , 0.47-.48, repeated]

To keep flying, a Swainson’s Thrush needs to access extra water that’s stored in the proteins that make up its internal organs, and especially in its muscles. Metabolizing this muscle tissue generates five times more water than metabolizing the fat supplies. Experiments with Swainson’s Thrushes flying in wind tunnels, under moist and dry conditions, have shown that the birds have evolved to do precisely this. It’s a balancing act. They lose some muscle—but gain some water.

And are able to complete the ideal migratory path.

For BirdNote, I’m Michael Stein.

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Bird sounds provided by The Macaulay Library of Natural Sounds at the Cornell Lab of Ornithology, Ithaca, New York. Swainson’s Thrush [206453] recorded by Bob McGuire. BirdNote’s theme music was composed and played by Nancy Rumbel and John Kessler.Producer: John KesslerExecutive Producer: Dominic Black